Cathode for electric discharge devices



June 14, 1932. J w S 1,863,394

CATHODE FOR ELECTRIC DISCHARGE DEVICES Filed Dec. 28., 1929 Inventor:James W Case, by

His Abner-neg.

Patented June 14, 1932 UNITED STATES PATENT OFFICE JAMES W. CASE, OFSCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COM- PANY, ACORPORATION OF NEW YORK CATHODE FOR ELECTRIC DISCHARGE DEVICESApplication filed December 28, 1929. Serial No. 417,240.

My'invention relates to electrodes for electric discharge devices andhas for its principal object the provision of an improved cathodearrangement for mercury arc recti- I fiers.

Large power rectifiers which are provided with metallic tanks havehitherto been provided with porcelain insulators positioned be-- tweenthe tank and the metallic cup which holds the mercury cathode. Thisinsulator is exposed to a high temperature gradient during operation andbeing fragile is liable to breakage either because of physical shock orbecause of uneven expansion and contrac- 16 tion.

In accordance with my invention these disadvantages are obviated by theprovision of means including a porous and rugged insulator positionedbetween the tank and cathode and surrounded by a vacuum chamber whichalso encloses the cathode.

My invention will be better understood from the following descriptionwhen considered together with the accompanying drawing and its scopewill be pointed out in the appended claims.

The single figure in the accompanying drawing illustrates in crosssection, a cathode structure built in accordance with my invention and afragmentary cross section of the rectifier tank to which it is attached.

Referring thereto in detail, 1 illustrates a cross section of the lowerend of the rectifier tank. The mercury cathode 2 is contained in ametallic cup or dish 3 which is provided with a water jacket 4:. Thedish 3 is separated by an insulator 6 from a metallic flange 5, which isarranged to be attached to the tank 1. This insulator is preferablycomposed of layers of mica which tend to make the insulator porous yetimpervious to mercury vapor. The dish 3 is rigidly bolted to flange 5 byinsulated bolts 7 and a jacket 8 is arranged to surroimd both theinsulator and the dish. This jacket is Welded to flange 5 and insulatedfrom the cathode terminal 9 and water jacket connections 10 by gas impervious vitreous seals. Seals of this type are made by compressing aplastic mass of vitreous material such as a mixture of mica and glass,between two metallic members I which are then joined respectively to themembers to be insulated from each other.

It will be evident from the above description that the cathode dish 3can be cooled by passing cooling fluid through the jacket 4 andinsulated connections 10. Since the insulator 6 is porous, the spacebetween jackets 4L and 8 is evacuated through the insulator 6 and ismaintained at a pressure substantially that of the main tank. Thisevacuated space or chamber provides heat insulation between the cathodeand the room temperature said dish and flange, and an evacuated cham bersurrounding said insulator and dish.

2. In an electric discharge device provided with a metallic tank, acathode structure including a flange attached to said tank, a metallicdish attached to said flange and provided with a cathode terminal, aporous insulator between said dish and flange, and a jacket surroundingsaid insulator and dish.

3. In a mercury arc rectifier provided with a metallic tank, a cathodestructure including a flan e attached to said tank, a metallic dishprovi ed with a water jacket and cathode terminal, an insulator betweensaid dish and flange, an evacuated chamber surrounding said insulatorand dish, and insulated connections for said water jacket extendingthrough said evacuated chamber.

In witness whereof, I have hereunto set my hand this 27th day ofDecember, 1929.

JAMES W. CASE.

